Apparatus for launching at least one plug into a tubular in a wellbore

ABSTRACT

An apparatus for launching at least one plug into a tubular in a wellbore, in certain aspects, the apparatus having a hollow upper section with at least first and second upper ports one above the other, a landing seat, and a first fluid displaceable member below the second upper port, the hollow lower section adapted to retain a plug and having a first lower port and a landing collar for the fluid displaceable member.

This invention relates to an apparatus for launching at least one pluginto a tubular in a wellbore, for example, a liner in an oil or gaswell. Wiper plugs are generally, but not exclusively used in connectionwith the cementing of such liners.

In the cementing of casing and liners in a wellbore, the annular spacebetween the casing/lining and the wellbore is filled with apredetermined quantity of a cement mixture which, after hardening,retains the casing/liner in place in the wellbore.

The cement mixture is pumped in at the top end of the casing or liner,down to the lower end thereof and out into and up the annular space onthe outside of the casing/liner.

Before the cement mixture is pumped into the casing/liner, it is usual,although not essential, for a first plug to be introduced at the top ofthe casing/liner which slides in a sealing-tight relationship againstthe casing/liner. When a predetermined quantity of cement mixture hasbeen introduced into the casing/liner, a second plug is introduced inorder to separate the cement mixture from a well liquid which isthereafter supplied under pressure to drive the cement mixture into thecasing/liner. The first plug is adapted to be opened for cement mixtureto flow therethrough when the plug lands at the lower end of thecasing/liner. The cement mixture thereafter flows through the firstplug, comes into contact with and displaces liquid which is in theannular space, and pressure from the liquid supplied from the surfaceacts behind the second plug and pushes thereon until it lands on thefirst plug.

Sometimes it is disadvantageous to have direct contact between thecement mixture and the liquid in the well and the annular space, sinceundesirable chemical reactions may take place. In that case a suitableliquid is pumped ahead of the cement mixture. This is done byintroducing into the casing/liner a first plug, a separating liquid, asecond plug, cement mixture, and finally a third plug. Therefore, thecement mixture substantially only comes into contact only with theseparating liquid. It may also be advantageous to pump a number ofspecial liquids through the liner/casing, both before and after thecement mixture, thereby necessitating a number of further plugs.

Generally, in the cementing of liners use is made of plugs having acentral opening, so that the liquid can flow therethrough which areplaced at the top of the liner. When the plug is to be launched, asealing element such as a dart is introduced into the stream of liquidfrom the surface. The sealing element arrives on the plug and seals saidcentral opening, and the water pressure then drives the sealed plug downthe liner.

The above described design has been known to fail in use by eitherlaunching at least two plugs simultaneously, or by failing to launch anyplugs.

According to the present invention, there is provided an apparatus forlaunching at least one plug into a tubular in a wellbore, said apparatuscomprising a hollow upper section and a hollow lower section said hollowupper section comprising at least first and second upper portslongitudinally spaced therein, said second upper port being disposedabove said first upper port, a landing seat between said hollow uppersection and said hollow lower section, and a fluid displaceable memberretained below said second upper port, said hollow lower section adaptedto retain at least one plug and comprising at least a first lower portthereabove and a landing collar for said fluid displaceable member, thearrangement being such that in use, when the apparatus is installed atthe top of a liner and lowered into a wellbore, and a dart lands on saidlanding seat blocking said first upper port allowing a fluid pressuredifferential to be created about said fluid displaceable member throughsaid second upper port which displaces said fluid displaceable member tosaid landing collar, allowing a fluid pressure differential about saidplug through said first lower port to launch said plug.

Preferably, said apparatus further comprises a third upper port in saidhollow upper section above said second upper port and a second fluiddisplaceable member retained below said third port said hollow lowersection adapted to retain a second plug, and comprising a second lowerport thereabove, so that in use, a second dart lands on said first dartblocking said second upper port it allows a fluid pressure differentialto be created about said second fluid displaceable member through saidsecond upper port which displaces said second fluid displaceable memberto said first fluid displaceable member blocking said first lower port,allowing a fluid pressure differential about said second plug throughsaid second lower port to launch said second plug.

Advantageously, said fluid displaceable member is a sleeve which, inuse, substantially blocks the annulus between the apparatus and thetubular.

When the sleeves come into the lower position, they produce the requiredeffect by closing the liquid supply to the underside of the plug whichis to be discharged from the apparatus into the liner. The pressure onthe top side of the plug then displaces the plug downwards in theapparatus. The first sleeve closes the outlet of the annular space atthe bottom, the second sleeve closing ports which conduct liquid fromthe annular space to the underside of the second plug. A third sleevewill close ports which conduct liquid from the annular space to theunderside of a third plug, and so on.

Preferably, said fluid displaceable member is shear pinned to saidapparatus.

Advantageously, said landing seat blocks a central fluid path betweensaid hollow upper sections and said hollow lower sections.

Preferably, each port is the form of a horizontal row of ports.

Advantageously, said hollow upper section and said hollow lower sectionare of circular cross-section having equal outer diameters.

Preferably, the fluid displaceable member comprises a seal.

There is also provided a method for launching at least one plug usingthe apparatus defined hereabove.

For a better understanding of the present invention, reference will nowbe made, by way of example, to the accompanying drawings, in which:

FIG. 1 is a diagrammatic cross-sectional view of part of an apparatusaccording to the invention, including two plugs therein, in a startingposition;

FIG. 2 shows the apparatus of FIG. 1 after a first dart has landed inthe apparatus;

FIG. 3 shows the apparatus of FIG. 1 after a first sleeve has beendisplaced to a lower end of the apparatus;

FIG. 4 shows the apparatus after a lower plug has launched from theapparatus;

FIG. 5 shows the apparatus after a second dart has landed therein;

FIG. 6 shows the apparatus after a second sleeve has been displaced tothe lower end thereof; and

FIG. 7 shows the apparatus after a second plug has launched from theapparatus.

FIG. 1 shows a liner 1 in which an apparatus 2 according to theinvention is disposed.

The external diameter of the apparatus 2 is smaller than the internaldiameter of the liner 1, or may be of equal diameter to the liner 2 anddisposed in a connecting hub which is of larger diameter than theapparatus 2, so that an annular space 3 is formed between the liner 1and the apparatus 2.

A first and second sleeve 4, 5 are arranged to slide in sealing-tightrelationship against the apparatus 2 and the liner 1. The bottom of theapparatus 2 has an external annular flange 6 which prevents the sleeves4, 5 from being separated from the apparatus 2. The annular flange 6extends only a relatively small distance radially, so that liquid canpass between the annular flange 6 and the liner 1.

The apparatus 2 is divided by a partition 7 into 9 hollow upper section7 a and a hollow lower section 7 b the partition 7 blocks a centralfluid path 32 between the hollow sections 7 a, 7 b. A first plug 8 isarranged in the lower hollow portion of the apparatus 2, and a secondplug 9 is disposed thereabove. The plugs 8 and 9 generally comprise finswhich are adapted to expand from the internal diameter of the apparatus2 to the internal diameter of the liner 1 and to slide in sealing-tightrelationship against the internal surface of the liner 1. If theapparatus is arranged in a hub as described above, the plugs 8, 9 do nothave to be compressed in order to expand to a working diameter.

The apparatus 2 has five sets of opening or ports which provide a fluidflow path between the apparatus 2 and the annular space 3; two sets ofports are disposed in the lower portion of the apparatus 2, below thepartition 7. A first set of ports 10 is arranged above the first plug 8and below the second plug 9. Another set of ports 11 is placed above thesecond plug 9.

A third set of ports 12 is placed directly above the partition 7. Afourth set of ports 13 discharges above the first sleeve 4 and below thesecond sleeve 5, while a fifth set of ports 14 discharges above thesecond sleeve 5.

The sleeves 4, 5 are retained in the starting position shown in FIG. 1by shear pins 30, 31 respectively. Below the first and second plugs 8, 9the apparatus 2 has internally rounded annular flanges 17 and 18respectively of small radial extension. The annular flanges 17, 18prevent the plugs 8, 9 from dropping out of the apparatus 2. The plugs8, 9 can nevertheless pass the annular flanges 17, 18 when sufficientforce is applied thereto. The rounded annular flanges 17 may be of agreater size than that depicted in the figures.

The liner 1 is lowered into the well by means of a setting tool (notshown) which is coupled and pressure sealed in a known manner to the topend of the liner 1 and depends from a tool string (not shown); the toolstring is adapted to supply drilling liquid, cement mixture and otherfluids to the top end of the apparatus 2.

While the liner 1 is being lowered into the well to be suspended in acasing by a suspension system (not shown), a liquid, typically adrilling liquid, is continuously supplied to the apparatus 2. The liquidflows out of the third set of ports 12 into the annular space 3 and downalong the outside of the apparatus 2 and onwards down into the liner 1.

When it is desired to release the first plug 8, a first dart 15 isintroduced in to the tool string and pumped into the apparatus 2 whereit lands on the partition 7, blocking the third set of ports 12 (FIG.2). Liquid cannot flow out into the annular space 3, since only the setsof ports 13 and 14 are open in the upper portion of the apparatus 2. Theoperator then may have to increase the liquid pressure being pumped downthe tool string. The pressure above and below the second sleeve 5 willtherefore be in equilibrium, while the pressure above the first sleeve 4is greater than the pressure therebelow and therefore the first sleeve 4experiences an overall downward force so that the shear pins forretaining the first sleeve 4 are broken. Then the first sleeve 4 isdriven downwardly in the annular space 3 by hydraulic pressure until thefirst sleeve 4 stops against the external annular flange 6 at the bottomof the apparatus 2 (FIG. 3). Liquid in the annular space 3 is thenunable to flow past the lower end of the apparatus 2, but is forcedinwardly over the first plug 8 via the first set of ports 10. The liquidpressure above and below the second plug 9 remains in equilibrium. Theliquid pressure exerts an overall downwardly directed force on andlaunches the first plug 8, out into the liner 1, whereupon the fins ofthe first plug 8 expand and enter into sealing-tight relationship withthe liner 1 (FIG. 4). Liquid supplied from the surface into the top ofthe apparatus 2 flows out into the annular space 3 via the fourth set ofports 13 below the second sleeve 5, down in the annular space 3, intothe lower portion of the apparatus 2 via the first set of ports 10,through the lower end of the apparatus 2 and into the liner 1. Theliquid therefore drives the first plug 8 down the liner 1.

Subsequently, when it is desirable to introduce the second plug 9 intothe liner 1, a second dart 16 is introduced into the stream of liquid onthe surface, and when the dart 16 lands on the dart 15, the dart 16blocks the fourth set of ports 13 (FIG. 5). The operator increases theliquid pressure being pumped down the tool string. The liquid pressureabove the second sleeve 5 is now greater than the pressure therebelowand therefore experiences an overall downward force so that the shearpins retaining the sleeve 5 break. The second sleeve 5 is displaceddownwardly in the annular chamber 3 and lands on the first sleeve 4. Thesecond sleeve 5 then blocks the first set of ports 10 in the lowerportion of the apparatus 2, so that the hydraulic pressure will act onlyon the top side of the second plug 9 (see FIG. 6). The hydraulicpressure will push the second plug 9 down in the apparatus 2 and out ofthe hollow lower portion thereof, so that the second plug 9 enters theliner 1 and expands into sealing-tight relationship with the liner 1.Liquid is then supplied from the surface to the top of the apparatus 2,out into the annular space 3 via the fifth set of ports 14, into thelower portion of the apparatus 2 via the second set of ports 11, throughthe lower end of the apparatus 2 and into the liner 1 (see FIG. 7).Liquid which continues to be supplied drives the second plug 9 andtherefore also the preceding liquid and the plug 8 down in the liner 1.

Another modification is envisaged in that a depression may be disposedin the partition 7.

Various other modifications to the above described embodiment areenvisaged, such as providing the apparatus with an additional set ofports above the port 14 and a third retained sleeve and providing thelower portion of the apparatus with means to retain a third plug and afurther port thereabove, so that in use a third dart could be used tolaunch a third plug in a similar way to that described above. Theapparatus could also be adapted in this way to launch four or moreplugs.

The apparatus could be used to launch plugs or a combination of plugsand other types of plugs, such as those designed to remove cement thathas set on the inside of liners known as scraper plugs.

Whilst it is desirable that the sleeves 4 and 5 should seal against theliner 1 and the apparatus 2 it will be appreciated that the apparatus 2would still work tolerably if there is a small leak.

What is claimed is:
 1. An apparatus for launching at least one plug intoa tubular in a wellbore, said apparatus comprising a hollow uppersection and a hollow lower section, said hollow upper section comprisingat least first and second upper ports (12, 13) longitudinally spacedtherein, said second upper port (13) being disposed above said firstupper port (12), a landing seat (7) between said hollow upper sectionand said hollow lower section, and a first fluid displaceable member (4)retained below said second upper port (13), said hollow lower sectionadapted to retain at least one plug (8) and comprising at least a firstlower port (10) thereabove and a landing collar (6) for said fluiddisplaceable member (4), the arrangement being such that in use, whenthe apparatus is installed at the top of a liner and lowered into thewellbore, and a first dart lands on said landing seat (7) blocking saidfirst upper port (12), creating a fluid pressure differential aroundsaid first fluid displacement member (4) and through said second upperport (13), the fluid pressure differential being used to displace saidfirst fluid displacement member (4) to said landing collar (6), allowingthe fluid pressure differential about said plug through said first lowerport (10) to launch said plug, said apparatus further comprising a thirdupper port (14) in said hollow upper section above said second upperport (13) and a second fluid displaceable member (5) retained below saidthird port (14) said hollow lower section adapted to retain a secondplug (9), and comprising a second lower port (11) thereabove, so that inuse, when a second dart (16) lands on said first dart (15) blocking saidsecond upper port it allows a fluid pressure differential to be createdabout said second fluid displaceable member (5) through said secondupper port which displaces said second fluid displaceable member (5) tosaid first fluid displaceable member blocking said first lower port(10), allowing the fluid pressure differential about said second plug(9) through said second lower port to launch said second plug.
 2. Anapparatus as claimed in claim 1 wherein said fluid displaceable members(4, 5) each is a sleeve which, in use, substantially blocks the annulusbetween the apparatus (2) and the tubular (1).
 3. An apparatus asclaimed in claim 1 wherein said fluid displaceable members (4, 5) areshear pinned to said apparatus.
 4. An apparatus as claimed in claim 1wherein said landing seat (7) blocks a central fluid path between saidhollow upper section and said hollow lower section.
 5. An apparatus asclaimed in claim 1 wherein each port is the form of a horizontal row ofports.
 6. An apparatus as claimed in claim 1 wherein said hollow uppersection and said hollow lower section are of circular cross-sectionhaving equal outer diameters.
 7. An apparatus as claimed in claim 1wherein the fluid displaceable members each comprises a seal.
 8. Amethod for launching at least one plug, the method comprising launchingat least one plug into a tubular into a wellbore using an apparatus forlaunching at least one plug into a tubular in a wellbore, said apparatuscomprising a hollow upper section and a hollow lower section, saidhollow upper section comprising at least first and second upper ports(12, 13) longitudinally spaced therein, said second upper port (13)being disposed above said first upper port (12), a landing seat (7)between said hollow upper section and said hollow lower section, and afirst fluid displaceable member (4) retained below said second upperport (13), said hollow lower section adapted to retain the at least oneplug (8) and comprising at least a first lower port (10) thereabove anda landing collar (6) for said fluid displaceable member (4), thearrangement being such that in use, when the apparatus is installed atthe top of a liner and lowered into the wellbore, and a first dart landson said landing seat (7) blocking said first upper port (12), creating afluid pressure differential around said first fluid displacement member(4) and through said second upper port (13), the fluid pressuredifferential being used to displace said first fluid displacement member(4) to said landing collar (6), allowing the fluid pressure differentialabout said plug through said first lower port (10) to launch said plug,said apparatus further comprising a third upper port (14) in said hollowupper section above said second upper port (13) and a second fluiddisplaceable member (5) retained below said third port (14) said hollowlower section adapted to retain a second plug (9), and comprising asecond lower port (11) thereabove, so that in use, when a second dart(16) lands on said first dart (15) blocking said second upper port itallows a fluid pressure differential to be created about said secondfluid displaceable member (5) through said second upper port whichdisplaces said second fluid displaceable member (5) to said first fluiddisplaceable member blocking said first lower port (10), allowing thefluid pressure differential about said second plug (9) through saidsecond lower port to launch said second plug.
 9. An apparatus forlaunching at least one plug into a tubular in a wellbore, said apparatuscomprising a hollow upper section and a hollow lower section, saidhollow upper section comprising first and second upper ports (12, 13)longitudinally spaced therein, said second upper port (13) beingdisposed above said first upper port (12) in operation, a landing seat(7) between said hollow upper section and said hollow lower section, anda first fluid displaceable member (4) initially retained in a firstposition below said second upper port (13), said hollow lower sectionbeing adapted to retain the at least one plug (8) and comprising atleast a first lower port (10) thereabove and a landing collar (6) forreceiving said first fluid displaceable member (4) in a second position,the arrangement being such that, in use, when the apparatus is installedat the top of a liner and lowered into the wellbore, launching of saidat least one plug is effected by causing a first dart to land on saidlanding seat (7) so as to block said first upper port (12) and create afirst fluid pressure differential across said first fluid displaceablemember (4) by way of said second upper port (13), the fluid pressuredifferential serving to displace said first fluid displaceable member(4) to the second position on said landing collar (6), thus creating afluid pressure differential across said at least one plug by way of saidfirst lower port (10) to launch said at least one plug.
 10. An apparatusas claimed in claim 9 further comprising a third upper port (14) in saidhollow upper section above said second upper port (13) and a secondfluid displaceable member (5) retained below said third port (14) saidhollow lower section adapted to retain a second plug (9), and comprisinga second lower port (11) thereabove, so that in use, when a second dart(16) lands on said first dart (15) blocking said second upper port itallows a fluid pressure differential to be created about said secondfluid displaceable member (5) through said second upper port whichdisplaces said second fluid displaceable member (5) to said first fluiddisplaceable member blocking said first lower port (10), allowing thefluid pressure differential about said second plug (9) through saidsecond lower port to launch said second plug.
 11. An apparatus asclaimed in claim 9 wherein said fluid displaceable members (4, 5) eachis a sleeve which, in use, substantially blocks the annulus between theapparatus (2) and the tubular (1).
 12. An apparatus as claimed in claim9 wherein said fluid displaceable members (4, 5) are shear pinned tosaid apparatus.
 13. An apparatus as claimed in claim 9 wherein saidlanding seat (7) blocks a central fluid path between said hollow uppersection and said hollow lower section.
 14. An apparatus as claimed inclaim 9 wherein each port is the form of a horizontal row of ports. 15.An apparatus as claimed in claim 9 wherein said hollow upper section andsaid hollow lower section are of circular cross-section having equalouter diameters.
 16. An apparatus as claimed in claim 9 wherein thefluid displaceable members each comprises a seal.
 17. A method forlaunching at least one plug, the method comprising launching at leastone plug into a tubular into a wellbore using an apparatus for launchingat least one plug into a tubular in a wellbore, said apparatuscomprising a hollow upper section and a hollow lower section, saidhollow upper section comprising first and second upper ports (12, 13)longitudinally spaced therein, said second upper port (13) beingdisposed above said first upper port (12) in operation, a landing seat(7) between said hollow upper section and said hollow lower section, anda first fluid displaceable member (4) initially retained in a firstposition below said second upper port (13), said hollow lower sectionbeing adapted to retain the at least one plug (8) and comprising atleast a first lower port (10) thereabove and a landing collar (6) forreceiving said first fluid displaceable member (4) in a second position,the arrangement being such that, in use, when the apparatus is installedat the top of a liner and lowered into the wellbore, launching of saidat least one plug is effected by causing a first dart to land on saidlanding seat (7) so as to block said first upper port (12) and create afirst fluid pressure differential across said first fluid displaceablemember (4) by way of said second upper port (13), the fluid pressuredifferential serving to displace said first fluid displaceable member(4) to the second position on said landing collar (6), thus creating afluid pressure differential across said at least one plug by way of saidfirst lower port (10) to launch said at least one plug.